Wave guide attenuator apparatus



June 19, 1951 E. T. JAYNEs WAVE GUIDE ATTENUATOR APPARATUS 2 Sheets-Sheet 1 Filed Feb. 17, 19.45

2 Shee'ts--Shee'rl 2 E. T. JAYNES WAVE GUIDE ATTENUATOR APPARATUS INVE v-0 wm! 7 JA Y/VES ATTORNEY June 19, 1951 Filed Feb. 17,1945l Patented June 19, 1951 UNITED WAVE GUIDE ATTENUATOR APPARATUS Edwin T. Jaynes, Anacostia, D. C., assigner to The Sperry Corporation, a corporation of Dela- Ware Application February 17, 1945, Serial No. 578,390

11 Claims.` (Cl. 178-44) The present invention relates to electromagnetic energy transmission devices, and more particularly to hollow pipe wave guide attenuating devices.

An object of the present invention is to provide an improved hollow pipe wave guide attenuator.

A further object is to provide a hollow pipe wave guide attenuator capable of accurate adjustment and of reliable attenuation variation characteristics.

It is well known that a hollow pipe wave guide, while a highly eicient conductor of electromagnetic energy oi" wavelengths shorter than a critical value often referred to as the cut-off wavelength, determined by the internal dimensions of the guide, is an excellent attenuator of electromagnetic energy of a Wavelength longer than the cut-01T wavelength of the wave guide. For example, an air-filled hollow pipe of S-inch inside diameter attenuates ultra high frequency.

energy of wavelengths shorter than 5 inches or 12.7 centimeters, in accordance with an attenuation constant far smaller than l-0 decibel per foot of length of the wave guide. On the other hand, such a 3-inch inside diameter hollow pipe attenuates electromagnetic energy of wavelengths appreciably greater than 5 inches by an attenuation constant in excess of 120 decibels per foot of length of the wave guide through which the electromagnetic energy is transmitted.

Variable attenuators have been devised to make use of the relatively high attenuation of wave guides operated at wavelengths in excess of the cut-off wavelength-the critical value of wavelength in the vicinity of which the attenuation per unit length of the wave guide rises steeply from an extremely low attenuation value to a substantially constant and quite appreciable value of approximately 32 decibels per unit length of' the' wave guide equal to the inside diameter thereof'.

For variation of the attenuation provided in devices of this type, apparatus usually is provided for varying the distance in the wave guide through which is transmitted electromagnetic energy of wavelength greater than the cut-off of the wave guide. Ordinarily, such apparatus takes the form of a mechanical arrangement for varying the distance in the wave guide between an input coupling element and anoutput coupling element.

A disadvantage of an attenuator of the above type is that in cases where a compact attenuator structure is desirable as, for example, a structure employing a l-inch inside diameter air-filled wave guide for attenuating wavelengths appreciably in excess of 2 inches (or appreciably in excess of 5 centimeters?, the attenuation per inch of distance along the cut-off wave guide is approximately 32 decibels per diameter, i. e., approximately 32 decibels per inch of length therealong. Thus, it is seen that a variation of the distance between the energy input coupling member and the energy output coupling member of g1g of an inch in a l-inch wave guide results in a change of attenuation of 1 decibel. For many purposes, where high accuracy of both the attenuation adjustment and the attenuation readings is desirable, such a great change of attenuation relative to a small movement of thevadjustable member is found unsatisfactory for accurate and reliable performance.

Accordingly, it is anobject of the present invention to provide a cut-off. wave guide attenuator having an attenuation adjustment arrangement wherein large movements of an adjustable member result in relatively small changes of attenuation.

If a wave guide is excited in only one excitation mode by energy of a wavelength in excess of the cut-off wavelength for that mode, the attenuation in decibels varies linearly with variation of the length of the energy transmission path therethrough. If the wave guide is excited inv a plurality of modes, on the other hand, the attenuation in decibels varies non-linearly with variation of the length of the energy transmission path. Such attenuation non-linearity dueto multiple-mode excitation ordinarily is slightly objectionable in a cut-off Wave guide attenuator, but it becomes especially objectionable in an attenuator intended for very precisel variation of attenuationand dependable indication of the attenuation variations effected therein.

Therefore, it is another object of the present invention to provide wave guide coupling members so arranged as to suppress the excitation of the wave guide in excitation modesY other than a single predetermined mode.

For reliability, high accuracy, and convenience of installation, it is desirable that cut-off 'wave guide attenuators be so constructed and arranged as to provide stationary cable input and output connectors, so that the attenuator may be installed with rigid connections to other ultra high frequency devices independently of variation of the distance between the in-put coupling member and the output coupling member in the Cut-off wave guide.

Accordingly, a further object of the present invention is to provide improved wave guide attenuator coupling members, permitting adjustment of the distance through which energy is transferred by the cut-oit wave guide without any resultant change of the position of the input and output cable connectors or terminals of the attenuator.

In accordance with the present invention, a movable member, which may take the form of a relatively thin-walled metal tube, for example, may be inserted telescopically'between the inner surface of a stationary cut-off wave guide and the outer surface of a tubular coupling member associated therewith. Such a thin-walled metal tube may be moved in a direction parallel to the axis of the cut-oi Wave guide, so as to vary the projection of the thin-walled metal tube into the cut-ofi wave guide beyond the end of the tubular coupling member. rlihe portion of the thinwalled metal tube thus extending Within the cutoff wave guide beyond the coupling member operates substantially as a movable cut-oli wave guide portion having a slightly smaller diameter than the stationary cutbff wave guide and, accordingly, having a slightly greater attenuation constant per unit length thereof.

By movement of the thinwalled tube farther into the cut-off wave guide, the attenuation provided between the above-mentioned tubular coupling member and a further coupling member positioned at the opposite end of the stationary cut-off Wave guide at a fixed distance from the tubular coupling member is gradually increased by virtue of a reduction of the distance through which the wave energy is propagated through the exposed portion of the stationary cut-OIT wave guide and an equal increase of the distance in the slightly higher attenuation thin-Walled metal tube through which the energy must travel.

In accordance with one feature of the present invention, a Vernier calibration scale and a vernier drive member may be associated with such a thin-walled metal tube, while a wide-range attenuation calibration scale and a rough adl justment mechanism may be associated with one of the above-mentioned energy coupling members, for variation of the total distance between the coupling members through which the energy must be transmitted through the successive cutoff Wave guide portions.

With the high accuracy obtainable with a vernier attenuation adjustment and indicating arrangement as generally7 discussed above, any nonuniformity of attenuation per unit length along a uniform-diameter section of cut-OIT wave guide becomes particularly objectionable. As a further feature of the present invention, therefore, the tubular coupling member discussed above may comprise a section of conductive tubing illed with solid dielectric material having such a dielectric constant in relation to its diameter as to provide ecient transmission therethrough in a predetermined excitation mode of the electromagnetic energy supplied to the cut-off wave guide. The dimensions and the properties of the dielectric material employed in this coupling member are so chosen that energy of only the desired mode of excitation of the cut-01T Wave guide is efficiently transmitted therethrough; While for energy of modes of excitation which, if transmitted eiciently through the coupling member,l would excite the cut-off Wave guide in other than the desired excitation mode, the coupling member is a cut-E Wave guide. Thus, the solid dielectric 4 l filled Wave guide input coupling member serves as a lter, passing only energy of a desired excitation mode for the cut-OIT wave guide, and preventing excitation of the cut-oil wave guide with appreciable energy in any other mode.

The above objects and general description of the present invention will be claried, and further objects will become apparent, by reference to the following detailed description of the present invention, taken in conjunction with the drawings, wherein:

Fig. 1 is a side elevation, partly in section, of one embodiment of the present invention;

Fig. 1A is a fragmentary cross-sectional View illustrative of a modied form of the invention;

Fig. 2 is a cross-sectional view taken along the line 2 2 in Fig. 1;

Fig. 3 is a Side elevation, partly in section, and Fig. 4 is a plan view, partly in section, of a further embodiment of the present invention.

Fig. 5 is a side elevation, partly in section, of a further embodiment of the present invtntion. The structure to the right of line A-A is arranged as shown in Fig. l.

In Figs. l and 2 is shown an attenuator comprising a base II supporting the fixed portions and the control elements of a cut-off wave guide attenuator constructed in accordance with the present invention. A hollow pipe wave guide I2 having a circular cross-section, for example, is secured to the base II by a supporting bracket I6. The hollow pipe wave guide I2 is provided With an input coupling member I3 and an output coupling member I arranged for connection to a high frequency energy source I5 and a load I6, respectively.

Energy from source I5 may be conducted through a coaxial transmission line having an outer conductor 2B and an inner conductor Il into a further coaxial transmission line formed by a reentrant tubular conductor I8 operatingk in conjunction with an extension I9 of the hollow pipe wave guide I2. A conductive sleeve 2l, telescopically slidable along the reentrant tubular conductor I8, is connected through a radially extending conductor 22 to a tubular conductor 23 arranged in slidable relation with the tubular extension i9 of the hollow pipe wave guide I2. A

dissipator disc Z may be provided at a distance.

of one-fourth of the Wavelength of the energy derived :from source I5 from the radially extending conductor 22 for providing a load connected between sleeve 2l and conductor 23 in addition to the load presented by the radially extending conductor 22, such that standing waves are minid mized in the coaxial transmission lines I8, I9 and 2|, 23. For this purpose, also, the conductive sleeve 2| may be arranged to extend axially beyond the tubular conductor 23 by a distance equal to one-fourth of the wavelength of the energy derived from source I5. ri"he movable structure 2|, 22, 23, 24 cooperating with conductor I8 and tubular extension i5 serves as the input coupling member I3 for introducing or feeding energy into the cut-oir wave guide l2.

The coaxial transmission line 223, !'I is preferably joined to the line lIS, I9 at a distance of substantially one-fourth of the wavelength` of the energy derived from source I5 from the end of the line I8, I9, and a conductive disc 25 preferably is connected between the tubularI conductor I8 and the extension I9 of the hollow' pipe wave guide to prevent radiation of ultra high frequency energy from'the end of the lineI I8, I9 and to alford suitablev mechanical support of the reentrant tubular conductor I8.

The portion of the input coupling member comprising the conductive sleeve 2 I, the tubular conductor 23, the radially extending conductor 22 and the dissipator disc 24 may be moved axially along the wave guide I2, effectively lengthening or shortening the distance between coupling members I3 and I4, through a range of movement determined by the length of thev sleeve 2i. For this purpose, a rod 21 which may be made of conductive or non-conductive material, as desired, may be inserted` slidably through the reentrant tubular conductor I8 and may be connected mechanically to the conductive sleeve 2I at the end thereof adjacent the radially extending conductor 22. If desired, a bushing 28 may be rigidly fastened to the end of the rod 'i' extending beyond the transmission line i8, I9 and the bushing 28 may be provided with a rack 29 for cooperation with the pinion 3I to afford fine mechanical adjustment of the movable coupling member described above. Pinion 3| may be arranged on a shaft 32 supported in a suitable bearing by a bracket 33 extending upward frome base II, and the shaft 32 may be provided with a manual adjustment knob 34.

If desired, a pointer 35 may be fastened to the bushing 28 and arranged for cooperation with a calibrated wide-range stationary attenuation scale 35 for indicating the variation of attenuation resulting from the adjustment of the movable coupling member I3.

The output coupling member I4 for extracting energy from cut-off Wave guide I2 may' comprise a section of coaxial transmission line having an outer tubular conductor 38 and an inner conductor 39. The conductor 39 may be bent at one end and connected as shown at 34 to the tubular outer conductor 38, to form a radially extending conductor portion coupled to the wave guide'I2. The output coupling member I4 may be supported by a bracket 42 positioned near oneV end of the base Il- In accordance with a major feature of the present invention, a movable member isA provided for eiecting a predetermined shift in the attenuation per unit length along a variablev length portion of the cut-01T wave guide I2 between the input coupling member I3 and the output coupling member I4. For example, a conductive sleeve 43, such as a thin-walled metal tube. may be provided in telescopic relation with the hollow pipe wave guide I2 and the tubular coupling member I4, for providing along the por-v tion of conductive sleeve 43 extending beyondv the tubular coupling member I4 an attenuation per unit length, which is greater by a predetermined margin than the attenuation per unit length along the portion of cut-off wave guide I2 between the end of sleeve 43 and the cou'-V pling member I3. For example, a conductive sleeve 43 having an inside diameter of fifteensixteenths of an inch would provide an attenuation constant of approximately 34 decibels per inch along the length thereof, while the portion of the wave guide I2 extending between the end of the conductive sleeve 43 and the coupling member I3, if of one-inch inside diameter, provides an attenuation of the order of 32 decibels per inch. Thus, if the coupling members I3 and I4 are separated by a given distance, andthe conductive sleeve 43 is moved towardthe cou-` pling memberl I3, the attenuation inserted 'be-.v

\ to drive the sleeve 43 to a desired position for- 6, tween the source I5 and theload I8 would be increased by approximately 2 decibels per inch of movement of the conductive sleeve 43.

As shown in Fig. 1, a portion of the conductive sleeve 43 extending outside the hollow pipe wave guide i2 may be provided with a rack 44 for cooperation with a pinion 45, and also with a pointer 46 for cooperation with a calibration scale 41. By rotation of pinion 45, the attenua-- tion of the energy supplied to the load IB may be gradually varied over a narrow Vernier range, as indicated by the pointer 45 and scale 41.

If desired, large changes of attenuation may be eiiected by the rotation of pinion 3I, providing relatively large movements of the input coupling member I3. Then, after the member I3 is positioned for a desired approximate attenuation value, the pinion 45 may be rotated more accurate control of the attenuation of energy supplied from source I5 to load I6. It will be seen that rotation of pinion 3| varies the distance between the coupling member I3 and the coupling member I4, while the rotation ofV pinion 45 leaves the total distance between the coupling members fixed while varying difierentially the lengths of two successive or cascade portions along cut-off wave guide I2 characterized by two slightly different attenuation constants.

If desired, and as shown in Fig. 1A, sleeve .43Y may be made of a solid dielectric material, rather than a conductive material, with a resultant increasevof the cut-01T wavelength along the portion of the hollow pipe wave guide I2 occupied by the sleeve 43', and thus with a resultant decrease, rather than increase, of the attenuation per unit length in the portion of the wave guide I2 occupied by the sleeve 43 as compared to the attenuation per unit length within the portion ofthe wave guide I2 between the end of sleeve 43' and the input coupling member I3.

With the sleeve 43 composed of a dielectric material, energy loss due to ultra high frequency potential diiference between the outside of the tubular conductor 38 and the inside of the hollow pipe wave guide i2 may be prevented from producing appreciable radiation or energy leakage by making the length of the coupling member I4V extending within the hollow pipe wave guide I2 appreciable, and thus providing an axially extensive energy attenuating path between the wave guide I2 and the output coupling member If desired, the input and output coupling members associated with the cut-off hollow pipe wave guide may be formed as wave guide elements fil-led with solid dielectric material of a high dielectric constant. An embodiment of this invention having such wave guide coupling members is illustrated in Figs. 3 and 4. As shown in these iigures, a base H supports a hollow pipe wave guide I2 through a bracket I. A rst coupling memberr I4', comprising a tubular conductor 38 filled by a solid dielectric body 50, is ixedly supported from base I I by bracket 42. A second wave guide coupling member is formed by a tubular extention I9' of the hollow pipe Wave guide I2 substantially filled by a dielectric rod 5I, which may be slidably supported in the tubular extension i9 for variation of the effective position of the coupling member I3', and thus of the effective distance between the coupling members I3' and I4.

Coaxial transmission line connectors 52, 53 and,

54, 55 may be provided for conduction of ultra high frequency energy from a source I5 to the variable attenuator system and from the attenuator system to a load I6'. The outer conductor 52 of the rst coaxial line, shown connected to source I5', may be connected to the tubular conductor 38 forming the conductive outer sheath of the wave guide coupling member I4', While the inner conductor 53 of the rst coaxial line is extended through the tubular conductor 38 through a suitable passage in the dielectric body 50 along the diameter thereof and connected to the conductor 38' at a point 49 opposite the junction of tubular conductor 38 with the outer conductor 52 of the iirst coaxial line.

Similarly, the second coaxial line connector 54, 55, shown connected to load I 6', includes a junction of the outer conductor 54 with the extension I9' of hollow pipe wave guide I2', which serves as the tubular conductor cooperating with dielectric rod 5I to form an eiiicient wave guide for conduction of energy of the wavelength of source I5. The inner conductor 55 of the second coaxial line extends through the extension I9 of hollow pipe wave guide I2 along the diameter thereof parallel to conductor 53 within tubular conductor 38.

To permit the movement of the dielectric rod 5I along the axis of the wave guide I2', a slit 56 is provided in rod 5I for passage therethrough of the inner conductor 55 of the second coaxial connector. Also, in order to prevent the transmission of ultra high frequency energy from the conductor 55 along dielectric rod 5I through the open end 51 of the tubular extension I9', a conductiv-e septum 58 may be tted into the tubular extension I9' of the hollow pipe wave guide I2'. This septum 5S is preferably arranged in the diametral plane including the conductors 53 and 55, spaced one-fourth of the wavelength of source I5 from the conductor 55, and extending an appreciable distance toward the open end 5I of the extension i9. In the above-described position, the edge of septum 58 adjacent conductor 55 forms a short-circuiting reiiector for cooperation therewith, to arrest energy flow toward open end 5'I. Furthermore, the septum 58 divides the portion of the wave guide coupling member I9', 5 I occupied thereby into two parallel wave guide portions, one positioned above the other and each having a semicircular cross-section, each f these wave guides being cut-off at the Wavelength o source I.

If desired, a block of dielectric material 59 may be cemented into place in the end of the dielectric rod 5I, filling the slit at the end of the rod and aflording mechanical reinforcement thereto.

By virtue of the high dielectric constants of the bodies 55 and 5 I the rst wave guide coupling member extending between conductor 53 and the end 6I of the coupling member I4', and the second wave guide coupling member extending between the end 62 of body 5I and the conductor 55, are rendered ecient wave guide conductors for ultra high frequency energy of the wavelength of source I5.

A feature of the attenuator structure shown in Figs. 3 and 4 is the pre-attenuation provided by the first coupling member I4', employed as shown in Figs. 3 and 4 as the input coupling member, of excitation energy components in modes other than the desired mode of excitation of the cutoi wave guide i2. For this purpose, the dimensions of the coupling member I4 and the characteristics of the dielectric material 50 are chosen for eicient transmission of the energy from source I5' only in the longest-wavelength mode permitted in a cylindrical wave guide, a mode sometimes referred to as the TE1,1 mode.

Thus, even though ultra high frequency current produced in the conductor 53 by source l5 may excite the solid dielectric filled wave guide in a plurality of modes in addition to the TE1,1 mode for which the wave guide is designed, the attenuation along the solid dielectric filled wave guide of the TEL1,1 mode energy is almost negligible, whereas other modes of excitation are greatly attenuated along the coupling member I4,so that their amplitude in the vicinity of the end 6I is negligible. Thus, only the desired excitation mode is provided at the end 6I of member I4" for introduction of energy into the cutoff wave guide I2.

The structure shown in Figs. 3 and 4 may be operated with the energy source connected to the coaxial connector 54, 55 and the load connected to the coaxial connector 52, 53. The preattenuation of excitation modes other than the desired TEM mode is then eected in the dielectric-nllecl wave guide portion of tubular extension I8 exten-ding between the conductor 55 and the end 52 of rod 5I, in a manner similar to that described with respect to the coupling member Ill when source I5 is connected thereto.

If the energy source is to be coupled to the connector 54,V 55, the dielectric body 5I should be so arranged that, at the maximum attenuation adjustment thereof, an appreciable length of the dielectric body 5I extends between the end 62 and the conductor 55.

Although the illustrative embodiments of the presentinvention show a movable tubular sleeve of dielectric or conductive material as a Vernier adjusting element, it will readily be seen that the principle of the invention could be applied in a variety of other forms. For example, the cutoff wave guide may be of rectangular or elliptical cross-section, and a movable member for Vernier attenuation adjustment may comprise a bar or rod of material movable within the cut-off wave guide but of carefully chosen characteristics, such that the portion of the cut-01T wave guide occupied by the bar or rod is not converted to an efficient energy conductor at the Wavelength of the energy source. Furthermore, the internal cross-sectional shape of the cut-OIT wave guide might be altered from a normal shape to a predeterminedly altered shape along a variable length thereof for carrying out the principles taught in the foregoing objects and description. In Fig. 5 the shape of cut-01T waveguide I2 is altered by movable member I0 over a portion of its length 43"'.

Since many changes could be made in the above construction and many apparently widely different embodiments of this invention could be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. Attenuating apparatus for electromagnetic energy of at least a predetermined Wavelength, comprising a hollow pipe wave guide for conducting electromagnetic energy of at least said predetermined wavelength, said wave guide being so dimensioned as to provide substantially constant attenuation per unit length therealong of electromagnetic energy of longer wavelength than 9 said predetermined wavelength, a movable sleeve telescopically tted within one end of said hollow pipe wave guide, rst coupling means in said movable sleeve in energy-interchanging relation with said hollow pipe wave guide, and second coupling means engaging said hollow pipe wave guide in energy-interchanging relation therewith, whereby said hollow pipe wave guide conducts energy between said rst and second coupling means; said first coupling means comprising a solid dielectric lled wave guide extending within said movable sleeve and said second coupling vmeans comprising a cable having a first conductor connected to said hollow pipe wave guide at a first point thereon and a second conductor extending through said hollow pipe wave guide adljacent said rst point and connected thereto at -a second point opposite said rst point, and Ya dielectric ro/d slidably supported within vsaid hollow pipe wave guide, said rod having a longitudinal slit Ytherewithin through which said second conductor extends, whereby said rod may be moved -along said hollow pipe wave guide for varying the length of said rod extending between said second conductor and said lrst coupling means.

2. Ultra high frequency apparatus comprising: a hollow pipe wave guide; a reentrant tubular conductor connected to said hollow pipe wave guide and extending through a predetermined distance therewithin; a movable member having an outer tubular portion slidably supported in contact with the inner surface of said hollow pipe wave guide, an inner tubular portion slidably supported in contact with said reentrant tubular conductor, and a radially extending conductor connecting said inner tubularportion to said outer tubular` portion; and a rod coupled to said movable member and extending through yand beyond said reentrant tubular conductor whereby the position of said movable member within said hollow pipe wave guide may b e varied by move'- ment of said rod.

3. In combination, a hollow pipe wave guide, a conductive sleeve telescopically iitted within said wave guide and arranged for movement therewithin, and a solid dielectric lled wave guide telescopically -tted within said movable sleeve, said movable sleeve being arranged for movement with respect to both said hollow pipe wave guide and said solid dielectric filled wave guide.

4. Ultra high frequency energy transmission apparatus comprising a hollow pipe wave guide, means coupled to said wave guide in energyinterchanging relation therewith, a transmission line having a rst conductor connected to said hollow pipe wave guide at a rst point thereon and a second conductor extending through said hollow pipe wave guide adjacent said first point and connected thereto at a side opposite said rst point, and a dielectric rod slidably supported within said hollow pipe wave guide, said rod having a longitudinal slit therein through which said second conductor extends, whereby said rod may be moved along said hollow pipe wave guide for varying the length of the portion of said rod extending between said second conductor and said energy-interchanging means.

10 netic energy of wavelength longer than said predetermined wavelength, a movable sleeve telescopically fitted within one end of said hollow pipe wave guide, rst coupling means in said movable sleeve in energy-interchanging relation with said hollow pipe wave guide, and second coupling means engaging said hollow pipe wave guide in energy-interchanging relation therewith, said second coupling means comprising a reentrant tubular conductor connected to said hollow pipe wave guide and extending therethrough Y ported .in contact with said reentrant tubular 5. Attenuating apparatus for electromagnetic conductor connected to said outer tubular portion through a radially extending conductor, and a rod coupled to said movable member and extending beyond .said hollow pipe wave guide through said reentrant tubular conductor, whereby the position of said movable member within said hollow pipe wave guide may be varied by movement of a portion of said rod extending externally of said hollow pipe wave guide.

6. Attenuating apparatus for electromagnetic energy of at least a predetermined wavelength, comprising a hollow pipe wave guide for conducting electrcmagnetic energy of at least said predetermined wavelength, said wave guide being so dimensioned as to provide substantially constant attenuation per unit length for electromagnetic energy of wavelength longer than said predetermined wavelength, a movable sleeve telecopically tted within one end of said hollow pipe wave guide, rst coupling means in said movable sleeve in energy-interchanging relation with said hollow pipe wave guide, said first coupling means comprising a section of coaxial transmission line having an outer conductorrand an inner conductor extending along said movable sleeve, said inner conductor being connected to said outer conductor at the end thereof adjacent said hollow pipe wave guide, and second coupling means engaging said hollow pipe wave guide in energy-interchanging relation therewith,said second coupling means comprising a reentrant tubular conductor connected to said hollowpipe wave guide and extending therethrough toward said movable sleeve, a movable member having an outer tubular portion slidably supported in contact with said hollow pipe wave guide and an inner tubular portion slidably supported in contact with said reentrant tubular conductor and connected to said outer tubular portion through a radially extending conductor, and a rod coupled to said movable member and extending through and beyond said reentrant tubular conductor, whereby the position of said movable member within said hollow pipe wave guide may be varied by movement of a portion of said rod extending externally of said hollow pipe wave guide.

'7. Attenuating apparatus for electromagneticI energy of at least a predetermined wavelength, comprising a hollow pipe wave guide for conducting electromagnetic energy of at least said predetermined wavelength, said wave guide being so dimensioned as to provide substantially constant attenuation per unit length for electromagnetic energy of wavelength longer than said predetermined wavelength, a movable sleeve telescopically tted within one end of said hollow pipe wave guide, first coupling means in said movable sleeve in energy-interchanging relation with said hollow pipe wave guide, and second coupling means engaging said hollow pipe wave guide in energy-interchanging relation therewith, said second coupling means comprising a transmission line having a iirst conductor connected to said hollow pipe wave guide at a point thereon and a second conductor extending through said hollow pipe wave guide adjacent said point and connected thereto at a second point thereon opposite said first point, and a dielectric rod slidably supported within said hollow pipe wave guide, said rod having a longitudinal slit therein through which said second conductor extends, whereby said rod may be moved along said hollow pipe wave guide for varying the length of said rod extending between said second conductor and said first coupling means.

8. Attenuating apparatus for electromagnetic energy of at least a predetermined wavelength, comprising a hollow pipe wave guide for conducting electromagnetic energy of at least said predetermined wavelength, said wave guide being so dimensioned as to provide substantially constant attenuation per unit length for electromagnetic energy of wave length longer than said predetermined wavelength, a movable sleeve telescopically tted within one end of said hollow pipe wave guide, rst coupling means in said movable sleeve in energy-interchanging relation with said hollow pipe wave guide, and second coupling means engaging said hollow pipe wave guide in energyeinterchanging relation therewith, said second coupling means comprising a conductive metal septum extending across said hollow pipe wave guide, a transmission line having a rst conductor connected to said hollow pipe wave guide at a rst point thereon and a second conductor extending through said hollow pipe wave guide adjacent said rst point and connected thereto at a point thereon, said second conductor lying within the plane of said septum between said septum and said first coupling means, and a dielectric rod slidably supported within said hollow pipe wave guide, said rod having a longitudinal slit therein through which said septum and said second conductor extend, whereby said rod may be moved along said hollow pipe wave guide for varying the length of said rod extending between said second conductor and 'said rst coupling means.

9. Ultra-high-frequency apparatus comprising a hollow pipe wave guide; a tubular conductor within said hollow pipe wave guide and extending through a predetermined distance therewithin; a movable member having an outer tubular portion slidably supported in contact with the inner surface of said hollow pipe wave guide, an inner tubular portion slidably supported in contact with said tubular conductor, and a radially extending conductor connecting said inner tubular portion and said outer tubular portion; and means connected to said movable member and extending through and beyond said tubular conductor for varying the position of said movable member.

10. High frequency apparatus comprising a hollow pipe wave guide section adapted to propagate energy therealong at a predetermined operating frequency, an energy-coupling means con- REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 2,197,123 King Apr. 16, 1940 2,232,179 King Feb. 18, 1941 2,376,785 Krasik May 22, 1945 2,407,267 Gnzton Sept. 10, 1946 2,411,553 Ramo Nov. 26, 1946 2,423,396 LinderV July 1, 1947 2,427,098

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